Diplomacy is the art and practice of conducting negotiations between representatives of states. It usually refers to the conduct of international relations through the intercession of professional diplomats with regard to a full range of topical issues. Diplomacy entails influencing the decisions and conduct of foreign governments and officials through dialogue, negotiation, and other nonviolent means. Diplomacy is the main instrument of foreign policy, which consists of the broader goals and strategies that guide a state's interactions with the rest of the world. International treaties, agreements, alliances, and other manifestations of foreign policy are usually negotiated by diplomats prior to endorsement by national politicians. Diplomats may also help shape a state's foreign policy in an advisory capacity. Since the early 20th century, diplomacy has become increasingly professionalized, being carried out by accredited career diplomats supported by staff and diplomatic infrastructure, such as consulates and embassies. Subsequently, the term 'diplomats' has also been applied to diplomatic services, consular services and foreign ministry officials more generally. Some of the earliest known diplomatic records are the Amarna letters written between the pharaohs of the Eighteenth dynasty of Egypt and the Amurru rulers of Canaan during the 14th century BC. Peace treaties were concluded between the Mesopotamian city-states of Lagash and Umma around approximately 2100 BCE. Following the Battle of Kadesh in 1274 BC during the Nineteenth dynasty, the pharaoh of Egypt and the ruler of the Hittite Empire created one of the first known international peace treaties, which survives in stone tablet fragments, now generally called the Egyptian–Hittite peace treaty. The ancient Greek city-states on some occasions sent envoys to each other in order to negotiate specific issues, such as war and peace or commercial relations, but did not have diplomatic representatives regularly posted in each other's territory. However, some of the functions given to modern diplomatic representatives were in Classical Greece filled by a proxenos, who was a citizen of the host city having a particular relations of friendship with another city, often hereditary in a particular family. In times of peace diplomacy was even conducted with rivals such as the Achaemenid Empire of Persia, though the latter eventually succumbed to the invasions of the Macedonian king Alexander the Great. The latter was also adept at diplomacy, realizing that in order to conquer certain territories it was important for his Macedonian and subject Greek troops to mingle and intermarry with native populations. For instance, Alexander even took a Sogdian woman of Bactria as his wife, Roxana, after the siege of the Sogdian Rock, in order to quell the region (which had been troubled by local rebels such as Spitamenes). Diplomacy was a necessary tool of statecraft for the great Hellenistic kingdoms that were established, such as the Ptolemaic Kingdom and Seleucid Empire, who fought several wars in the Near East and often negotiated a peace treaty through alliances through marriage. Relations with the government of the Ottoman Empire (known to Italian states as the Sublime Porte) were particularly important to Italian states. The maritime republics of Genoa and Venice depended less and less upon their nautical capabilities, and more and more upon the perpetuation of good relations with the Ottomans. Interactions between various merchants, diplomats and clergy men hailing from the Italian and Ottoman empires helped inaugurate and create new forms of diplomacy and statecraft. Eventually the primary purpose of a diplomat, which was originally a negotiator, evolved into a persona that represented an autonomous state in all aspects of political affairs. It became evident that all other sovereigns felt the need to accommodate themselves diplomatically, due to the emergence of the powerful political environment of the Ottoman Empire. One could come to the conclusion that the atmosphere of diplomacy within the early modern period revolved around a foundation of conformity to Ottoman culture. One of the earliest realists in international relations theory was the 6th century BC military strategist Sun Tzu (d. 496 BC), author of The Art of War. He lived during a time in which rival states were starting to pay less attention to traditional respects of tutelage to the Zhou Dynasty (c. 1050–256 BC) figurehead monarchs while each vied for power and total conquest. However, a great deal of diplomacy in establishing allies, bartering land, and signing peace treaties was necessary for each warring state, and the idealized role of the 'persuader/diplomat' developed. From the Battle of Baideng (200 BC) to the Battle of Mayi (133 BC), the Han Dynasty was forced to uphold a marriage alliance and pay an exorbitant amount of tribute (in silk, cloth, grain, and other foodstuffs) to the powerful northern nomadic Xiongnu that had been consolidated by Modu Shanyu. After the Xiongnu sent word to Emperor Wen of Han (r. 180–157) that they controlled areas stretching from Manchuria to the Tarim Basin oasis city-states, a treaty was drafted in 162 BC proclaiming that everything north of the Great Wall belong to nomads' lands, while everything south of it would be reserved for Han Chinese. The treaty was renewed no less than nine times, but did not restrain some Xiongnu tuqi from raiding Han borders. That was until the far-flung campaigns of Emperor Wu of Han (r. 141–87 BC) which shattered the unity of the Xiongnu and allowed Han to conquer the Western Regions; under Wu, in 104 BC the Han armies ventured as far Fergana in Central Asia to battle the Yuezhi who had conquered Hellenistic Greek areas.